DE 102 60 741 A1 describes a process as mentioned above and a respective plant in which hot gas with a temperature of about 1130° C. is generated in a combustion chamber upstream of the reactor and supplied to the reactor. Inside the reactor, this hot gas then can be cooled to about 750° C., for instance by contact with the cooler substances to be treated and/or by mixing with fluidizing gas. However, the hot gas enters the reactor with a comparatively high temperature and in said reactor gets in contact with the solids to be treated, which on the one hand can lead to local overheating and on the other hand also greatly stresses the components of the reactor.
EP 0 630 683 B1 discloses the introduction of hot gas into a reactor, wherein the hot gas is cooled by solid particles inside the reactor. In addition, cooling panels can be provided in the reactor.
In some applications, for instance when calcining clay, the temperature inside the reactor should not be above 700° C. Therefore, for instance in the processes mentioned above, problems arise in such applications when the fluidizable substances to be treated get in contact with the distinctly hotter waste gas of a combustion chamber. For such applications, such as the calcination of clay, conventional inexpensive fuels such as natural gas, petroleum or coal therefore cannot be directly burnt in the reactor. Thus, only a fuel such as butane, which ignites at lower temperatures, can also be used for a direct combustion inside the reactor space. Such fuels, however, which burn at lower temperatures, are comparatively expensive.
In other applications, hot gases are created and will be used in the downstream process parts as hot as possible in order to introduce the heat into these process parts.
The above-mentioned plants, in which hot gas is introduced into the reactor interior with temperatures of 500 to 1600° C., for example, 1000 to 1500° C., are furthermore expensive to manufacture because the gas supply tube, through which the waste gas of the combustion chamber or from other processes is passed, must be made of a heat-resistant material such as high-temperature resistant steel. Due to the great temperature differences with respect to other components of the plant, high thermal stresses can also occur.
An aspect of the present invention is to provide a process and a plant as mentioned above, which provide for the use of inexpensive fuels or hot waste gases and at the same time allow a gentle treatment of fluidizable substances in the reactor, wherein the loads acting on the reactor or the components remain limited.